1. Field of the Invention
This invention relates generally to vertical-takeoff-and-landing (VTOL) airplanes; and more particularly to tail-sitting aircraft capable of hovering flight, generally vertical takeoff and landing, and substantially horizontal forward flight.
2. Prior Art
Two types of prior aircraft are pertinent to my invention:
ducted -fan craft, such as the French Coleopter (FIG. 8) and the 1972 Shorts Skyspy; and PA1 "free wing" or "floating wing" craft in which the wing pivots about a spanwise axis, and is free to float in response to gusts. FIGS. 9 through 12 show a craft of this type, designed by Spratt. PA1 "Power plant: One SNECMA Atar 101E V turbojet engine (8,157 lb. 3,700 kg st). PA1 "Diameter of wing: 10 ft 6 in (3.20 m). PA1 "Length: 26 ft 31/2 in (8.022 m). PA1 "Accomodation: Pilot only. PA1 "Special design features: Annular wing of light alloy construction, consisting of two skins and internal structure (chord 9 ft 10 in, 3.0 m). Retractable foreplanes in fuselage nose. Cruciform fins and rudders to provide directional control in all axes. Four oleo-pneumatic landing legs mounted on trialing-edge of wing, small castoring wheels with rubber tyres. Tilting pilot's seat which could be ejected in an emergency. PA1 "History: Initial tests with the `Atar Volant` pilotless and piloted test vehicles proved the ability of a vertically-mounted turbojet to raise a VTOL aircraft safely from the ground, to accelerate it is vertical flight to a speed where it could become airborne like a conventional aircraft, and to return it to the ground in a vertical descent. SNECMA then built a prototype research aircraft around this type of power plant. Known as the C.450-01 Coleoptere, this prototype was basically similar to the C.400 P-3 piloted `Atar Volant`, but was fitted with an annular wing to permit transition into horizontal flight. The airframe, built by the Nord company in its Chatillonsous-Bagneux works, was intended for tests at subsonic speeds. Directional control at take-off and landing was by pneumatic deflection of the main jet efflux, directional control during normal horizontal flight was by four swiveling fins equally spaced around the rear of the annular wing. Under an agreement signed in 1958, the Federal German Ministry of Defence collaborated with SNECMA in this research programme. The C.450-01 made the first free vertical flight on May 6, 1959 at Melun-Villaroche, but on July 25, during a transition from vertical to horizontal flight, control of the aircraft was lost and it crashed from 250 ft (75 m). Although the aircraft was destroyed the pilot ejected successfully. Testing the Coleopiere, however, was considered to have been successful despite the accident." PA1 "The GEMINI TURBOPROP-350 is a new, innovative, single-engine, special performance aircraft. The GTP-350 is powered by Allison's soon-to-be-certified turbine, the 225-B10, delivering 350 shaft horse power (SHP). Combining the 225-B10 with the low weight, high strength characteristics of Allied's SPECTRA and COMPET Fibers creates a high-performance state-of-the-art aircraft. What really sets the GTP-350 apart, however, is the patented Slaved Tandem Freewing design; this configuration provides dramatic safety improvements as well as giving the plane near vertical take-offs and landings (VTOL). This brochure tells the story of the revolutionary GEMINI TURBOPROP-350. . . . PA1 "The GEMINI TURBOPROP-350 (GTP-350) lineage began prior to World War II when George K. Spratt and Daniel R. Zuck independently invented pure `freewing` design aircraft. Spratt, the more active researcher or the two, has designed, built and flown more than a dozen freewing vehicles. Further development came in the 1950s and 60s when several other researchers--including teams from NASA, General Dynamics and Battelle Memorial Laboratories [--] reported the study, building and successful flying of freewing designs. "In early 1977, Edward H. Allen, Ph.D., a professional systems scientist and experienced pilot, began to examine freewing development and perform experiments that eventually led to the formulation of a new concept--the `Slaved Tandem Freewing` (STF) configuration. Dr. Allen believed that theoretically the new configuration could be shown to be 10 times safer than existing general aviation aircraft. As a result, when the U.S. Department of Transportation requested proposals in 1984 for innovative means to reduce accidents and increase the safety of vehicles, Dr. Allen submitted a proposal for developmental funding of the STF design. A feasibility study contract was awarded by the DOT and after evaluating the results of that study, a two-year, follow-on contract for additional development work was awarded--including the design, manufacture and testing of a manned prototype. The DOT-sponsored work included the testing of four subscale, remotely piloted research vehicles (RPRVs . . .)--the largest of which had a 17-foot wing span and weighed more than 100 pounds. The [RPRVs] served to demonstrate the concept and the GEMINI TURBOPROP-350 was born. PA1 "Construction of the full-scale manned prototype began early in 1987. Flight testing is scheduled to begin with ground tests and system check-out in October 1987, with the first flight the following month. PA1 "Ease of operation and inherent safety in vehicle design are the greatest strengths of the STF concept. Of primary importance is the fact that STF vehicles cannot be stalled or spun in the dramatic way that fixed wing aircraft can. In addition, the natural tendency of an STF system to reduce the shocks from sudden changes in wind direction--the `gust allevation` tendency--is as important as stall resistance. In aerodynamic vehicles, the freewing is comparable to an automobile's suspension system . . . : it provides a safe and comfortable flight." PA1 "Spratt Wing/Stout Skycar IV PA1 "Since 1930, famous American designer William B. Stout had been trying to develop an easy-to-fly `everyman's airplane` through his series of Skycars. At the end of World War II he teamed up with George Spratt of the Stout Research Division or Convair, who had been developing airplanes with movable wings for several years. The Spratt/Stout collaboration, identified as Skycar IV, was built by Convair when that firm became interested in flying automobiles in 1946. PA1 "The Spratt wing was similar to that of the Mignet Flying Flea in being the primary pitch control for the airplane, but did much more in that it was also pivoted in such a way that it could be banked to put the plane in a turn. The wing was mounted above an elongated auto-like body with a buried engine driving a pusher propeller at the rear through an extension shaft [see FIG. 13]. The fixed end finds were used for stability only, not control. With the movable wing, there was no need for elevators, rudder, or ailerons. PA1 "This proof-of-concept prototype concentrated more on the aerodynamic details than the automotive. Although this one, for which technical data is conspicuously absent, was abandoned, Mr. Spratt is still developing aircraft with his wing at this writing."
In operation near hover, for a given diameter and power, a ducted fan produces more static thrust than an unducted propeller. The Coleopter enjoys this important advantage. Following is an excerpt from Taylor, J. W. R., ed., Jane's Pocket Book of Research & Experimental Aircraft (1976), at page 221, on the "SNECMA C.450-01 Coleopterere". FIG. 8 has been adapted from page 220 of the same work.
In cruise, the Coleopter is handicapped by having a wingspan that is small (i.e., equal to the duct diameter). This small causes span the cruise induced drag (drag due to lift) to be unacceptably high.
Several free-wing aircraft have been proposed and built. I do not know of any that have claimed static-thrust capability, although a brochure of the Allen Aircraft Company does describe an aircraft with capability of takeoff and landing over short distances. Excerpts (not necessarily in their original order) follow.